Nautical Miles vs Kilometres

[Pablo]

Hi!

I suspect the SH3 developers used the metric system for measurement since that is the standard measure used by landlubbers worldwide - and let's face it, there are many more people who use the metric system for distance measurement than there are using nautical miles. Unfortunately, this leads to pretty complex conversions best helped by the use of a nomograph.

The basic problem is that a "nautical mile' (by definition) is an angular measure: the length of a line spanning one minute of one degree of arc on the earth's surface. This would be great if the earth were a perfect sphere, but it's not: it is an "oblate spheroid" so the "real" length is shorter at the North and South Pole than it is at the equator.

To avoid mass confusion, the length of a nautical mile was standardized at 1852 km, which is the length of a nautical mile about half-way between the Poles and the Equator.

This yields the following conversions:

1 nautical mile = 1.852 km = approx. 1.15 statute miles

Pablo

[snitzel]

I'd rather have a mod that gets rid of knots/miles and shows the speeds in km/h and m/s

In fact I think they should have used two rulers. For large scale maps, use nautical miles to make it easy to plot convoys. For zoomed in maps, use kilometres (or optionally miles/yards for those backwards people ) to make it easier to calculate torpedo travel times etc for really-manual-shots.

In all books I have read, the crew speaks about ships "two miles" or "four kilometres" away, but when they start to shoot at it, they say "range 2000m" or "range 3500 yards". Makes sense, doesn't it?

[TarJak]

Originally Posted by Pablo

Hi!

I suspect the SH3 developers used the metric system for measurement since that is the standard measure used by landlubbers worldwide - and let's face it, there are many more people who use the metric system for distance measurement than there are using nautical miles. Unfortunately, this leads to pretty complex conversions best helped by the use of a nomograph.

The basic problem is that a "nautical mile' (by definition) is an angular measure: the length of a line spanning one minute of one degree of arc on the earth's surface. This would be great if the earth were a perfect sphere, but it's not: it is an "oblate spheroid" so the "real" length is shorter at the North and South Pole than it is at the equator.

To avoid mass confusion, the length of a nautical mile was standardized at 1852 km, which is the length of a nautical mile about half-way between the Poles and the Equator.

This yields the following conversions:

1 nautical mile = 1.852 km = approx. 1.15 statute miles

Pablo

I think you'll find it was actually the Kriegsmarine that use the metric measurement as standard for it's maps so that they could plan combined ops with the Luftwaffe and the army who both used km and km/h as standards. The Kreigsmarine kpet to knots as this was the worldwide standard for measuring ship speed, but all their maps were in km.

[PapaCharlie]

Hi guys,

Thanks for the responds. I was a merchant officer myself, so I know about the definition of a nautical mile, statue mile and stuff (and sure, the NM does not belong to the imperial system). If you use miles or kilometres, the problem of the earth being a sphere remains the same. It all depends of the charts you use.
I concider the map in SHIII a Mercator projection. You only get into trouble with that chart if you cross the ocean from east to west or vice-versa. Then a straight line from A to B is not the shortest way.
I was just wondering if there was a mod for it. Some of you are able to build mods, why hasn't anybody thought of a mod for converting miles into kilometres or the other way round? I cannot believe that in navigation on board a U-boat, the crew worked with knots as unit for speed and kilometres as unit of distance. That is asking for trouble and mistakes.
By the way, did you know that the Dutch and Germans (and Svcandinavians perhaps) also used a Geographical Mile or German mile, being 4 nautical miles? I know the used it in the age of square rigged sailing. Don't know if it was still in use in WOII. For those who are intrested, here is a link to a site to convert metric to imperial or nautical measurements:
http://www.squarerigged.nl/papa/dimen/conv.htm

But nevertheless, it's a great game. I am on my way home now, with my conningtower severely damaged. To late diving for a plane spotted. Damn planes!!


We'll meet again, dont know where, don't know when...

Papa Charlie

[_Seth_]

Wow, PapaCharlie! Excellent site, mate! I didnt know about that German mile, btw.. Always good to learn something new, mate!!

[Martin1813]

Originally Posted by Pablo

The basic problem is that a "nautical mile' (by definition) is an angular measure: the length of a line spanning one minute of one degree of arc on the earth's surface. This would be great if the earth were a perfect sphere, but it's not: it is an "oblate spheroid" so the "real" length is shorter at the North and South Pole than it is at the equator.

The problem is the same for the 'metre'. It's the 1/10,000,000 of a quarter of a meridian.


I agree with Papa Charlie. It would be a usefull mod. It'd be more logical.
but the conversion NM/Km is quite easy to do

however, there are excellent conversion charts in nots of modpacks.

[irish1958]

Here is what I do. Double the knots and use that for my Km distance. If I am feeling especially compulsive that day, I might subtract about 10% of the result to get my distance. When you consider the effect of wind, tide, zig-zagging, instrument error, etc. you have a fairly accurate distance. Besides, if you are attacking a convoy and want to get in front of them, it is best to overestimate your distance.